Electrolyte formulations for lithium ion batteries

ABSTRACT

Electrolyte solutions including additives or combinations of additives that provide low temperature performance and high temperature stability in lithium ion battery cells.

BACKGROUND OF THE INVENTION

The present invention is in the field of battery technology and, moreparticularly, electrolyte formulations that enable both low temperatureand high temperature operation of lithium ion batteries.

Certain applications for lithium ion batteries require wide operatingtemperature ranges. In general, the power capability of lithium ionbatteries suffers at low temperature due to one or more of the followingfactors: 1) an increase in viscosity of the electrolyte resulting inslower lithium ion diffusion; 2) a decrease in the ionic conductivity ofthe electrolyte; 3) a decrease in ionic conductivity of the solidelectrolyte interphase (SEI) on the anode; and 4) a decrease in thediffusion rate of lithium ions through the electrode materials,especially the anode materials.

In the past, solutions to the problems associated with operating alithium ion battery at low temperature have involved adding solventsthat have very low melting points and/or low viscosity to theelectrolyte formulation. Such additional solvents can help prevent theelectrolyte solution from freezing or having substantially increasedviscosity at low temperatures. However, such additional solvents tend tobe detrimental to the high temperature performance of a lithium ionbattery, and in particular the high temperature stability on cycling orstorage.

Certain of the shortcomings of known electrolyte formulations areaddressed by embodiments of the invention disclosed herein by, forexample, improving power performance at low temperature withoutsubstantially decreasing high temperature stability on storage.

BRIEF SUMMARY OF THE INVENTION

According to certain embodiments of the invention, electrolyteformulations include a lithium salt, an organic solvent, and anadditive. The additive includes a boron-containing compound selectedfrom the group consisting of diborons and borates. In some embodiments,the additive includes tris(2,2,2-trifluoroethyl)borate,bis(neopentylglycolato)diboron, or bis(trimethylene)diborate.

In some embodiments, the electrolyte formulation includes a secondadditive, which includes one or more of lithium bis(oxalato)borate,4-nitrophenyl 2-(trimethylsilyl)ethyl carbonate, cesium nitrate, maleicanhydride, tris(trimethylsilyl)phosphate, and trimethylsilylpolyphosphate.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A and 1B illustrate low temperature and high electrochemicalperformance characterization of battery cells assembled to containelectrolyte solutions made from formulations of certain embodiments ofthe invention and control electrolyte solutions.

FIGS. 2A and 2B illustrate low and high temperature electrochemicalperformance characterization of battery cells assembled to containelectrolyte solutions made from formulations of certain embodiments ofthe invention and control electrolyte solutions.

FIGS. 3A and 3B illustrate low and high temperature electrochemicalperformance characterization of battery cells assembled to containelectrolyte solutions made from formulations of certain embodiments ofthe invention and control electrolyte solutions.

FIGS. 4A and 4B illustrate low and high temperature electrochemicalperformance characterization of battery cells assembled to containelectrolyte solutions made from formulations of certain embodiments ofthe invention and control electrolyte solutions.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein. Each term is further explained andexemplified throughout the description, figures, and examples. Anyinterpretation of the terms in this description should take into accountthe full description, figures, and examples presented herein.

The singular terms “a,” “an,” and “the” include the plural unless thecontext clearly dictates otherwise. Thus, for example, reference to anobject can include multiple objects unless the context clearly dictatesotherwise.

The terms “substantially” and “substantial” refer to a considerabledegree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

The term “about” refers to the range of values approximately near thegiven value in order to account for typical tolerance levels,measurement precision, or other variability of the embodiments describedherein.

A rate “C” refers to either (depending on context) the discharge currentas a fraction or multiple relative to a “1 C” current value under whicha battery (in a substantially fully charged state) would substantiallyfully discharge in one hour, or the charge current as a fraction ormultiple relative to a “1 C” current value under which the battery (in asubstantially fully discharged state) would substantially fully chargein one hour.

To the extent certain battery characteristics can vary with temperature,such characteristics are specified at room temperature (about 25 degreesC.), unless the context clearly dictates otherwise.

Ranges presented herein are inclusive of their endpoints. Thus, forexample, the range 1 to 3 includes the values 1 and 3 as well asintermediate values.

The term “NMC” refers generally to cathode materials containingLiNi_(x)Mn_(y)Co_(z)O_(w), and includes, but is not limited to, cathodematerials containing LiNi_(0.33)Mn_(0.33)Co_(0.33)O₂.

A lithium ion battery implemented in accordance with embodiments of theinvention includes an anode, a cathode, and a separator that is disposedbetween the anode and the cathode. The battery also includes anelectrolyte formulation, which is disposed between the anode and thecathode. An electrolyte formulation can include one or more solvents andone or more lithium-containing salts. Examples of conventional solventsinclude nonaqueous electrolyte solvents for use in lithium ionbatteries, including carbonates, such as ethylene carbonate, dimethylcarbonate, ethyl methyl carbonate, propylene carbonate, methyl propylcarbonate, and diethyl carbonate.

The operation of the lithium ion battery is based upon intercalation andde-intercalation of lithium ions into and from the host materials of theanode and the cathode. Other implementations of the battery arecontemplated, such as those based on conversion chemistry. The voltageof the battery is based on redox potentials of the anode and thecathode, where lithium ions are accommodated or released at a lowerpotential in the former and a higher potential in the latter.

Examples of other suitable cathode materials include phosphates,fluorophosphates, fluorosulfates, fluorosilicates, spinels, lithium-richlayered oxides, and composite layered oxides. Further examples ofsuitable cathode materials include: spinel structure lithium metaloxides (e.g., LiMn₂O₄), layered structure lithium metal oxides (e.g.,LiNi_(x)Mn_(y)Co_(z)O₂), lithium-rich layered structured lithium metaloxides (e.g., Li₂MnO₃—LiNi_(x)Mn_(y)CoO₂), lithium metal silicates(e.g., Li₂FeSiO₄), lithium metal phosphates (e.g., LiFePO₄), metalfluorides, metal oxides, sulfur, and metal sulfides. Examples ofsuitable anode materials include conventional anode materials used inlithium ion batteries, such as lithium, graphite (“Li_(x)C₆”), and othercarbon, silicon, or oxide-based anode materials.

In many lithium ion batteries using conventional electrolyteformulations, components within the electrolyte solution facilitate thein-situ formation of a protective film on or near an electrode duringthe initial battery cycling. This is referred to as a solid electrolyteinterphase (SEI) layer. The anode SEI can inhibit further reductivedecomposition of the electrolyte components.

In lithium ion batteries, low temperature performance is characterizedby measuring the area specific impedance (ASI), which includescontributions due to the electrode materials, the SEI layers formed onthose materials, and the bulk electrolyte properties. As this is ameasure of impedance, low ASI values are desirable.

High temperature performance is characterized by measuring the change inASI after storage at elevated temperature. Again, small changes in theASI after storage are desirable as such small changes would indicatestability of the cell while it is stored at elevated temperature.

At high temperature, stability of the battery cell can becomecompromised. Instability at high temperature is believed to be dueto: 1) increased reactivity of electrolyte with an active material; 2)accelerated decomposition of LiPF₆, which generates decompositionproducts that can be reactive with the both the electrolyte and theelectrode active materials. Parasitic reactions driven by thedecomposition products can result in loss of cell capacity and furtherdecomposition of any SEI.

Conventional electrolyte formulations with no additives can show goodlow temperature performance (as shown by low area specific impedance)because thin and/or poor SEIs are formed. Similarly, electrolyteformulations with conventional additives can also show good lowtemperature performance for the same reason (thin and/or poor SEIs).Thus, acceptable low temperature performance is apparently achieved withcertain additives even though these additives are not forming desirableSEIs. Yet, these formulations show very poor high temperature stability(as shown by high area specific impedance after high temperaturestorage). Thus, apparent acceptable low temperature performance does nottranslate into acceptable wide operating temperature performance.

Embodiments of electrolyte formulations disclosed herein address theproblem of achieving both low temperature power and high temperaturestability. Certain electrolyte additives present in the electrolyteformulation provide improvements to low temperature performance andimprove or maintain high temperature performance. Without being bound toa particular hypothesis, theory, or proposed mechanism of action, theperformance improvement of the additives is due to improvements in theSEI layer, specifically the SEI that forms on the graphite anode in thepresence of these additives.

In some embodiments, combinations of additives improve low temperatureperformance and improve or maintain high temperature performance ascompared to conventional electrolyte formulations (with or withoutconventional additives). Certain combinations disclosed herein can bethought of as being either SEI formers or SEI modifiers, andcombinations of these classifications of additives show benefits asdemonstrated by the data disclosed herein.

For example, in the class of SEI formers are additives such as lithiumbis(oxalate)borate (LiBOB), certain carbonates, 1,4-butane sultone, andmaleic anhydride. These SEI formers form passivation layers to protectthe graphite anode surface. In contrast, the class of SEI modifiersincludes additives that tend to react with pre-formed SEI or precursorsof SEI (such as the reductive decomposition product of ethylenecarbonate). The SEI modifiers improve the SEI physical properties (e.g.,thickness and uniformity) and SEI composition (e.g., the ratio ofinorganic to organic species and the ionic content). SEI physicalproperties and SEI composition determine the high temperature stabilityand low temperature impedance of the SEI. Generally speaking, SEIformers tend to show thicker SEI at higher additive concentration, whichoften results in better high temperature stability but worse lowtemperature power performance (likely due to thicker, higher impedanceSEI).

In certain embodiments of additive combinations disclosed herein, SEImodifiers include certain silicon-containing additives, certaininorganic salts, certain activated linear carbonates, and certainisocyanate-containing compounds. The silicon-containing additives mayreduce the LiF content of the anode SEI due to high reactivity betweensilyl ethers and fluorine ions, which would result in anode SEIcompositions with a lower ratio of inorganic to organic species. Theinorganic salts may alter the ionic content of the SEI. The activatedlinear carbonates and isocyanates can readily react with precursors ofSEI (e.g., reductive decomposition intermediates of ethylene carbonateor LiBOB) to modify the chemical composition of SEI. Thus, byintroducing SEI modifiers, formation of a thinner but more thermallystable SEI can be achieved. These SEI modifiers act to improve the anodeSEI generated by the SEI formers. However, as demonstrated herein anddescribed below, the classes of SEI formers and SEI modifiers act inspecific ways such that it is not obvious which members of each classwill work synergistically to provide the desired wide operatingtemperature performance.

In certain embodiments of additive combinations disclosed herein, theelectrolyte formulation includes certain boron-containing additives. Theboron-containing additives are often strong electrophiles. In otherwords, they readily react with reductive decomposition intermediatesfrom solvents and salts on the anode, which may result in a thinner butmore thermally stable SEI. Effective boron-containing additives arebelieved to be highly activated compounds that contain at least oneactivated B—O bond by either being attached to at least one fluorinatedsubstituent (e.g., fluorinated alkyl chain) or being part of a cyclicmoiety.

In some embodiments, the boron-containing additive is a compoundrepresented by structural formula (a):

where at least one of R₁, R₂ and R₃ includes a fluorine. R₁, R₂ and areindependently selected from the group consisting of substituted C₁-C₂₀alkyl groups, substituted C₁-C₂₀ alkenyl groups, substituted C₁-C₂₀alkynyl groups, and substituted C₅-C₂₀ aryl groups. At least one of thesubstitutions is a fluorine, and other additional substitutions arepossible, include further fluorine substitutions. Preferred embodimentsinclude tris(2,2,2-trifluoroethyl)borate and its derivatives.

In some embodiments, the boron-containing additive is a compoundrepresented by structural formula (b):

where X is oxygen or carbon and, independently, Y is oxygen or carbon.The remainder of the ring can be unsubstituted or include furthersubstitutions. The ring can have any number of members. Preferredembodiments include certain diboron structures. Preferred embodimentsinclude bis(neopentylglycolato)diboron and bis(trimethylene)diborate.

The following examples describe specific aspects of some embodiments ofthe invention to illustrate and provide a description for those ofordinary skill in the art. The examples should not be construed aslimiting the invention, as the examples merely provide specificmethodology useful in understanding and practicing some embodiments ofthe invention.

EXAMPLES Battery Assembly

Battery cells were formed in a high purity argon filled glove box(M-Braun, O₂ and humidity content <0.1 ppm). A LiNi_(x)Mn_(y)Co_(z)O₂(NMC, x+y+z=1) cathode material and a graphite (G) anode material wereused. Each battery cell includes the composite cathode film, apolyolefin separator, and composite anode film. The G:NMC capacity ratiois greater than 1 to help ensure no lithium deposition, particularly atlow temperatures (e.g., temperatures less than 25 degrees Celsius).Electrolyte formulations were made according to the ratios andcomponents described herein and added to the battery cell.

Electrolyte Solution Formulation.

Electrolyte formulas included a lithium salt and a solvent blend. Thelithium salt was LiPF₆, and was used at a concentration of 1.2M. Theformulations typically contained ethylene carbonate (EC), ethyl methylcarbonate (EMC), dimethyl carbonate (DMC), and methyl butyrate (MB) inthe ratio EC/EMC/DMC/MB (20/30/40/10 by volume).

Electrochemical Formation.

The formation cycle for NMC//G cells was was a 6 hour open circuitvoltage (OCV) hold followed by a charge to 4.1V at rate C/10, with aconstant voltage (CV) hold to C/20. The formation cycle was completedwith a C/10 discharge to 2.5 V. All formation protocols were run at roomtemperature.

Electrochemical Characterization.

Initial area specific impedance (ASI) was measured after setting thetarget state of charge (SOC) (by discharging the cell at rate of C/10)and then applying a 10 second pulse at a rate of 5 C. Low temperatureASI results were derived as follows: The cell was recharged to 4.1 V ata rate of C/5 at room temperature, with a CV hold at C/10 followed by aone hour OCV hold. Then, the ambient temperature was reduced to −25degrees Celsius, followed by a 12 hour OCV hold to allow the test systemtemperature to equilibrate. All discharges to the specified SOC whereconducted at −25 degrees Celsius at a rate of C/10, with a one hour restat the specified SOC. A discharge pulse at 50% SOC was done at a rate of2 C for 10 seconds, followed by a 40 second rest. ASI was calculatedfrom the initial voltage (V) prior to the pulse and the final voltage(V_(f)) at the end of the pulse according to Formula (1), where A is thecathode area and i is the current:

$\begin{matrix}{{{ASI}\left( {\Omega \cdot {cm}^{2}} \right)} = \frac{\left( {V_{i} - V_{f}} \right) \times A}{i}} & (1)\end{matrix}$

After full recharge to 4.1 V at room temperature, the cells were thenstored at 60 degrees Celsius at OCV for two weeks. After two weeks thecells were removed from high temperature storage and then allowed toequilibrate to room temperature. The ASI was then measured by the sameprotocol used to determine initial ASI (after setting the target SOC andthen applying a 10 second pulse at a rate of 5 C).

Results

FIGS. 1A and 1B illustrate electrochemical performance characterizationof battery cells assembled to contain electrolyte solutions made fromformulations of certain carbonate additives as compared to controlelectrolyte solutions. While vinylene carbonate (VC) is a commonly usedSEI additive in lithium ion batteries, other carbonate type additivesprovide improved low temperature power performance. The presence ofstrong electron-withdrawing functionality (such as fluorine) showed thebest improvements. Specific additives include4-nitrophenyl-2-trimethylsilyl ethyl carbonate (“NPTMSEC”) (structure(c)); allylmethyl carbonate (structure (d)); allylphenyl carbonate(structure (e)); and bis(pentafluorophenyl)carbonate (“BPFPC”)(structure (f)):

These additives also improved or maintained high temperature performancerelative to VC, as demonstrated in FIGS. 1A and 1B. FIG. 1A shows thearea specific impedance (ASI) at low temperature for certain electrolyteformulations containing carbonate additives. The control formulationcontains no additives. Two additional control additive formulations aredepicted (LiBOB and VC), both of which have higher impedances than theformulations with carbonate additives. FIG. 1B shows data collectedafter the high temperature storage described herein. Taken together,FIGS. 1A and 1B show that certain carbonate additives improve lowtemperature performance while maintaining, or not significantlydiminishing, the high temperature performance of the system.

FIGS. 2A and 2B illustrate electrochemical performance characterizationof battery cells assembled to contain electrolyte solutions made fromformulations of certain silicon-containing additives as compared tocontrol electrolyte solutions. The same controls are used as in FIGS. 1Aand 1B. Specific silicon-containing additives includetris(trimethylsilyl)phosphate (“TTMSPhate”) (structure (g));tris(trimethylsilyl)phosphite (“TTMSPhite”) (structure (h));trimethylsilyl polyphosphate (TMSpoly) (structure (i)); andtrimethylsilyl acrylate (“TMSA”) (structure (j)):

FIG. 2A shows the ASI at low temperature for certain electrolyteformulations including silicon-containing additives. FIG. 2B shows datacollected after the high temperature storage described herein. FIGS. 2Aand 2B show that certain silicon-containing additives improve lowtemperature performance while maintaining the high temperatureperformance of the system.

FIGS. 3A and 3B illustrate electrochemical performance characterizationof battery cells assembled to contain electrolyte solutions made fromformulations of certain inorganic salt additives as compared to controlelectrolyte solutions. These inorganic salt additives are used inaddition to the conventional LiPF₆ salt that serves as the lithium ionconductor in the electrolyte. The same controls are used as in FIGS. 1Aand 1B. Specific inorganic salt additives include carbonates (Li₂CO₃,Na₂CO₃, K₂CO₃), perchlorates (LiClO₄, NaClO₄), hexafluorophosphates(NaPF₆, CsPF₆), oxalates (Li₂C₂O₄, Na₂C₂O₄), and nitrates (NaNO₃,CsNO₃). FIG. 3A shows the ASI at low temperature for certain electrolyteformulations including inorganic salt additives. FIG. 3B shows datacollected after the high temperature storage described herein. FIGS. 3Aand 3B show that certain inorganic salt additives improve lowtemperature performance while maintaining, or not significantlydiminishing, the high temperature performance of the system.

FIGS. 4A and 4B illustrate electrochemical performance characterizationof battery cells assembled to contain electrolyte solutions made fromformulations of certain boron-containing additives as compared tocontrol electrolyte solutions. The same controls are used as in FIGS. 1Aand 1B. Specific boron-containing additives includetris(2,2,2-trifluoroethyl)borate (“TTFEB”) (structure (k));bis(neopentylglycolato)diboron (“BNpGB”) (structure (I)); andbis(trimethylene)diborate (“BTMB”) (structure (m)):

FIG. 4A shows the ASI at low temperature for certain electrolyteformulations including boron-containing additives. FIG. 4B shows datacollected after the high temperature storage described herein. FIGS. 4Aand 4B show that certain boron-containing additives improve lowtemperature performance while maintaining, or not significantlydiminishing, the high temperature performance of the system.

Area specific impedance is one measure of performance, but it is alsoimportant that the additives have no negative effects on initialdischarge capacities or coulombic efficiencies. Table 1 presentselectrochemical testing for certain additives and demonstrates that theadditives generally maintain the electrochemical performance of thecontrols while improving the wide operating temperature performance (asdescribed in other figures and tables herein). Two types of controlelectrolytes are included: (i) the electrolyte formulation with noadditives and (ii) the electrolyte formulation with control additives VCor LiBOB.

TABLE 1 First cycle capacities and coulombic efficiencies AdditiveConcentration Capacity CE Additive (%) (mAh/cm²) (%) Control with noadditives 0.0 0.99 86.1 Control with LiBOB 0.5 1.00 85.7 Control withvinylene carbonate 1.0 0.91 83.1 bis(pentafluorophenyl) carbonate 0.50.93 77.8 allyl phenyl carbonate 0.5 1.00 86.4 4-nitrophenyl2-(trimethylsilyl)ethyl 0.5 0.95 79.6 carbonate allyl methyl carbonate0.5 1.00 86.8 tris(trimethylsilyl) phosphate 0.5 0.97 88.2tris(trimethylsilyl) phosphite 0.5 0.99 88.1 trimethylsilylpolyphosphate 0.5 0.98 86.9 trimethylsilyl acrylate 2.0 1.00 88.3 cesiumhexafluorophosphate 0.5 1.00 88.4 sodium nitrate 0.5 0.99 83.2 sodiumoxalate 0.5 0.98 86.9 cesium nitrate 0.5 0.99 85.2 sodiumhexafluorophosphate 0.5 0.98 87.9 sodium percholorate 0.5 0.98 87.7lithium percholorate 0.5 0.98 87.7 potassium carbonate 0.5 1.00 88.2sodium carbonate 0.5 1.01 88.3 lithium carbonate 0.5 0.98 88.0 lithiumoxalate 0.5 0.98 86.8 bis(tri methylene)diborate 0.5 0.98 86.4bis(neopentyl glycolato)diboron 0.5 1.01 85.9tris(2,2,2-trifluoroethyl)borate 0.5 0.95 85.4

Table 2 provides the numerical data that is presented graphically inFIGS. 1A, 1B, 2A, 2B, 3A, 3B, 4A, and 4B.

TABLE 2 Summary of low and high temperature improvements AdditiveConcentration Low Temp 2nd Additive (%) ASI ASI Control with noadditives 0.0 223.0 99.7 Control with LiBOB 0.5 351.6 28.7 Control withvinylene carbonate 1.0 333.3 59.8 bis(pentafluorophenyl) carbonate 0.5222.2 105.6 (BPFPC) allyl phenyl carbonate 0.5 267.4 82.7 4-nitrophenyl2-(trimethylsilyl)ethyl 0.5 305.7 27.4 carbonate allyl methyl carbonate0.5 263.9 110.1 tris(trimethylsilyl) phosphate 0.5 255.2 23.5(TTMSPhate) tris(trimethylsilyl) phosphite 0.5 177.6 29.0 (TTMSPhite)trimethylsilyl polyphosphate (TMSpoly) 0.5 203.6 24.0 trimethylsilylacrylate (TMSA) 2.0 248.8 26.0 cesium hexafluorophosphate 0.5 201.3 94.3sodium nitrate 0.5 165.9 47.9 sodium oxalate 0.5 264.5 105.1 cesiumnitrate 0.5 227.0 28.1 sodium hexafluorophosphate 0.5 248.9 96.0 sodiumpercholorate 0.5 239.9 41.9 lithium percholorate 0.5 233.4 47.7potassium carbonate 0.5 208.0 92.1 sodium carbonate 0.5 242.4 137.7lithium carbonate 0.5 220.7 87.1 lithium oxalate 0.5 223.7 103.2bis(trimethylene)diborate 0.5 232.0 91.4 bis(neopentyl glycolato)diboron0.5 190.3 105.2 tris(2,2,2-trifluoroethyl) borate 0.5 171.2 86.4

While the additives described above can improve low temperatureperformance without substantially diminishing high temperaturestability, certain combinations of these additives with other additivescan also provide wide operating temperature performance improvements.Six of the above additives were chosen to combine with other additives:lithium bis(oxalato)borate (LiBOB),4-nitrophenyl-2-(trimethylsilyl)ether carbonate (NTSEC), CsNO₃, maleicanhydride (MA), tris(trimethylsilyl)phosphate (TTMSPhate), andtrimethylsilyl polyphosphate (TMSPoly). Specific additive combinationswere tested based on the improvements observed on each individualadditive. For example, if a given additive improves low temperatureproperties while a different additive only improves high temperatureproperties, the two additives were tested in combination. However, theresults from the combinations are not obvious. In other words, combininga given low temperature additive and a given high temperature additivedoes not necessarily result in a formulation with improved low and hightemperature properties.

Table 3 summarizes the performance of the six additives chosen as theprimary additive for the combination. These six additives demonstratehigh temperature stability improvements over a control electrolyteformulation that contains 1% VC and 0.5% LiBOB. Formulations containingthe additive combinations do not include VC or LiBOB with the exceptionof the target LiBOB combinations.

TABLE 3 Performance improvement of high temperature additives Cyc1 Cyc1High Temperature Conc. Capacity CE −25 C. 2nd Additive (wt. %) (mAh/cm²)(%) ASI ASI Control-1% VC + 0.5% 0.96 86.1 385 35 LiBOB lithiumbis(oxalato)borate 0.5 1.00 85.7 351.6 28.7 4-nitrophenyl 2- 0.5 0.9580.3 309.3 28.7 (trimethylsilyl)ethyl carbonate cesium nitrate 0.5 0.9985.2 227.0 28.1 maleic anhydride 0.5 0.92 81.8 340.5 26.3tris(trimethylsilyl) 0.5 0.97 88.2 255.2 23.5 phosphate trimethylsilylpolyphosphate 0.5 0.98 86.9 203.6 24.0

Surprisingly, as the results presented in Tables 4 through 9demonstrate, the additives that performed well according to Tables 1 and2 do not necessarily perform well in when combined with the sixadditives of Table 3.

Table 4 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with lithium bis(oxalato)borate. Certain of thecombinations, but not the majority of the combinations, show improvementover the control in both low temperature and high temperatureevaluation.

TABLE 4 Low temperature additives with LiBOB High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium oxalate 2 LiBOB 0.95 85.6 395.3 33.0 sodium percholorate 0.5LiBOB 0.93 87.1 348.5 34.6 sodium oxalate 0.5 LiBOB 0.93 86.0 329.3 35.3sodium 0.5 LiBOB 0.96 87.6 252.1 29.4 hexafluorophosphate sodiumcarbonate 0.5 LiBOB 0.93 86.1 417.1 35.6 potassium carbonate 0.5 LiBOB0.94 87.0 364.5 32.0 lithium percholorate 0.5 LiBOB 0.91 86.6 356.3 41.4lithium oxalate 0.5 LiBOB 0.95 86.9 334.3 28.4 lithium carbonate 0.5LiBOB 0.95 87.0 369.0 33.2 LiTFSI 0.5 LiBOB 0.92 85.4 308.8 43.4 cesiumoxalate 0.5 LiBOB 0.92 85.7 404.3 27.7 cesium nitrate 0.5 LiBOB 0.9687.8 312.6 50.9 tris(pentafluroophenyl) 2 LiBOB 0.87 78.8 351.5 45.4borane vinylboronic acid 2- 0.5 LiBOB 0.95 84.9 332.9 62.1methyl-2,4-pentanediol ester tris(2,2,2-trifluoroethyl) 0.5 LiBOB 0.9184.2 265.2 40.0 borate bis(trimethylene)diborate 0.5 LiBOB 0.93 85.7269.7 46.1 bis(neopentyl 0.5 LiBOB 0.95 85.8 258.7 43.7glycolato)diboron diallyl carbonate 0.5 LiBOB 0.95 86.3 349.3 32.8 allylphenyl carbonate 0.5 LiBOB 0.95 86.8 374.1 26.6 allyl methyl carbonate0.5 LiBOB 0.94 86.6 319.9 25.2 4-nitrophenyl 2- 0.5 LiBOB 0.90 80.9343.3 28.7 (trimethylsilyl)ethyl carbonate N,N-dimethylacetamide 0.5LiBOB 0.93 86.8 400.8 35.7 1-methyl-2- 0.5 LiBOB 0.90 84.7 435.2 36.5pyrrolidinone succinic anhydride 0.5 LiBOB 1.02 84.6 567.2 97.2ε-caprolactam 0.5 LiBOB 0.96 85.6 387.5 39.3 4-fluorophenyl 0.5 LiBOB0.92 83.4 350.1 32.8 isocyanate 3,6-dimethyl-1,4- 0.5 LiBOB 0.99 87.0534.4 101.2 dioxane-2,5-dione 1,4-butane sultone 0.5 LiBOB 0.98 86.4501.2 81.9 tris(trimethylsilyl) 0.5 LiBOB 0.89 82.8 276.4 126.8phosphate tris(trimethylsilyl) 0.5 LiBOB 0.97 86.6 253.0 22.8 phosphitetrimethylsilyl 0.5 LiBOB 0.97 85.4 300.5 21.9 polyphosphatetrimethylsilyl 0.5 LiBOB 0.91 84.4 341.8 53.0 isocyanate N,O- 0.5 LiBOB0.98 86.6 323.9 39.4 bis(trimethylsilyl)acetamide1-trimethylsilyl-1,2,4- 0.5 LiBOB 0.93 84.7 431.6 38.0 triazol malachitegreen 0.5 LiBOB 0.89 68.4 496.9 35.4 oxalate salt 1-(4,5-dihydro-1,3-0.5 LiBOB 0.95 82.0 379.1 69.1 thiazol-2-yl)piperidine oxalate

Combinations notable for their wide temperature range performanceimprovements include LiBOB and: sodium perchlorate, sodiumhexafluorophosphate, potassium carbonate, lithium oxalate, lithiumcarbonate, diallyl carbonate, allyl phenyl carbonate, allyl methylcarbonate, 4-nitrophenyl-2-(trimethylsilyl)ether carbonate,4-fluorophenyl isocyanate, tris(trimethylsilyl) phosphite, ortrimethylsilyl polyphosphate.

Table 5 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with 4-nitrophenyl-2-(trimethylsilyl)ethercarbonate. Certain of the combinations, but not the majority of thecombinations, show improvement over the control in both low temperatureand high temperature evaluation.

TABLE 5 Low temperature additives with NTSEC High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium perchlorate 0.5 NTSEC 0.93 80.8 354.1 35.6 sodium nitrate 0.5NTSEC 0.91 78.8 397.7 69.3 potassium carbonate 0.5 NTSEC 0.90 79.2 319.390.3 lithium perchlorate 0.5 NTSEC 0.90 78.1 338.5 27.2 lithium oxalate0.5 NTSEC 0.92 79.4 322.4 47.7 lithium carbonate 0.5 NTSEC 0.91 78.7315.6 114.8 cesium oxalate 0.5 NTSEC 0.93 79.8 369.4 50.3 cesium nitrate0.5 NTSEC 0.91 78.6 337.0 27.6 vinylboronic acid 2- 0.5 NTSEC 0.92 78.8309.5 147.2 methyl-2,4-pentanediol ester tris(2,2,2-trifluoroethyl) 0.5NTSEC 0.88 76.0 302.6 116.9 borate bis(trimethylene) 0.5 NTSEC 0.86 66.8337.3 87.3 diborate bis(neopentyl 0.5 NTSEC 0.93 80.3 634.6 134.1glycolato)diboron 2-allyl-5,5-dimethyl- 0.5 NTSEC 0.88 74.5 324.8 126.61,3,2-dioxaborinane diallyl carbonate 0.5 NTSEC 0.93 80.3 356.0 102.5N,N-dimethylacetamide 2 NTSEC 0.90 77.6 322.2 49.3 1-methyl-2- 0.5 NTSEC0.92 79.7 332.6 35.6 pyrrolidinone 4-fluorophenyl 0.5 NTSEC 0.92 79.7317.1 38.6 isocyanate 1,4-butane sultone 0.5 NTSEC 0.91 79.6 292.1 27.91-(4,5-dihydro-1,3- 0.5 NTSEC 0.91 66.8 342.8 50.4thiazol-2-yl)piperidine oxalate

Combinations notable for their wide temperature range performanceimprovements include NTSEC and: lithium perchlorate, cesium nitrate, or1,4-butane sultone.

Table 6 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with cesium nitrate. Certain of the combinations,but not the majority of the combinations, show improvement over thecontrol in both low temperature and high temperature evaluation.

TABLE 6 Low temperature additives with CsNO₃ High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium percholorate 0.5 CsNO₃ 0.95 86.1 284.8 51.1 sodium nitrate 0.5CsNO₃ 0.93 85.2 292.6 28.0 potassium carbonate 0.5 CsNO₃ 0.97 86.5 283.929.7 lithium percholorate 0.5 CsNO₃ 0.92 83.5 299.4 89.9 lithium oxalate0.5 CsNO₃ 0.95 85.1 301.1 40.2 lithium carbonate 0.5 CsNO₃ 0.96 85.7273.9 28.2 cesium oxalate 0.5 CsNO₃ 0.96 86.2 263.0 47.9 vinylboronicacid 2- 0.5 CsNO₃ 0.93 85.8 295.7 131.5 methyl-2,4-pentanediol estertris(2,2,2-trifluoroethyl) 0.5 CsNO₃ 0.90 84.1 226.2 56.8 boratebis(trimethylene) 0.5 CsNO₃ 0.93 86.3 293.7 95.4 diborate bis(neopentyl0.5 CsNO₃ 0.95 86.1 247.6 112.1 glycolato) diboron 2-allyl-5,5-dimethyl-0.5 CsNO₃ 0.94 86.4 270.5 139.2 1,3,2-dioxaborinane diallyl carbonate0.5 CsNO₃ 0.94 85.7 329.2 62.5 bis(pentafluorophenyl) 0.5 CsNO₃ 0.9178.9 256.3 45.7 carbonate N,N-dimethylacetamide 2 CsNO₃ 0.95 85.4 297.448.8 1-methyl-2- 0.5 CsNO₃ 0.95 86.0 315.6 36.3 pyrrolidinone4-fluorophenyl 0.5 CsNO₃ 0.95 86.0 337.0 25.4 isocyanate 1,4-butanesultone 0.5 CsNO₃ 0.96 86.6 299.9 25.5 1-(4,5-dihydro-1,3- 0.5 CsNO₃0.91 78.7 356.0 90.6 thiazol-2-yl)piperidine oxalate

Combinations notable for their wide temperature range performanceimprovements include CsNO₃ and: sodium nitrate, potassium carbonate,lithium carbonate, 4-fluorophenyl isocyanate, or 1,4-butane sultone.

Table 7 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with maleic anhydride. Certain of thecombinations, but not the majority of the combinations, show improvementover the control in both low temperature and high temperatureevaluation.

TABLE 7 Low temperature additives with MA High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium percholorate 0.5 MA 0.88 82.9 402.2 32.5 sodium nitrate 0.5 MA0.87 80.6 487.2 57.8 potassium carbonate 0.5 MA 0.91 82.6 358.8 35.8lithium percholorate 0.5 MA 0.89 82.3 387.3 26.6 lithium oxalate 0.5 MA0.88 81.6 336.7 33.4 lithium carbonate 0.5 MA 0.90 81.8 399.9 34.5cesium oxalate 0.5 MA 0.89 81.9 375.0 23.0 cesium nitrate 0.5 MA 0.9381.9 390.9 33.7 vinylboronic acid 2- 0.5 MA 0.93 82.4 408.2 66.7methyl-2,4-pentanediol ester tris(2,2,2-trifluoroethyl) 0.5 MA 0.90 81.6283.6 39.8 borate bis(trimethylene) 0.5 MA 0.89 81.4 309.9 56.5 diboratebis(neopentyl 0.5 MA 0.88 81.4 325.7 74.8 glycolato)diboron2-allyl-5,5-dimethyl- 0.5 MA 0.89 81.2 471.8 112.7 1,3,2-dioxaborinanediallyl carbonate 0.5 MA 0.90 82.1 476.0 55.0 bis(pentafluorophenyl) 0.5MA 0.90 79.7 402.0 29.8 carbonate N,N-dimethylacetamide 2 MA 0.89 81.9353.4 35.5 1-methyl-2- 0.5 MA 0.89 81.0 351.6 62.9 pyrrolidinone4-fluorophenyl 0.5 MA 0.90 79.6 367.4 65.5 isocyanate 1,4-butane sultone0.5 MA 0.89 81.6 336.8 43.2 1-(4,5-dihydro-1,3- 0.5 MA 0.89 79.7 410.139.8 thiazol-2-yl)piperidine oxalate

Combinations notable for their wide temperature range performanceimprovements include maleic anhydride and: lithium oxalate or cesiumoxalate.

Table 8 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with tris(trimethylsilyl)phosphate. Certain of thecombinations, but not the majority of the combinations, show improvementover the control in both low temperature and high temperatureevaluation.

TABLE 8 Low temperature additives with TTMSP High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium percholorate 0.5 TTMS 0.95 88.2 257.9 37.8 Phate sodium nitrate0.5 TTMS 0.93 85.8 260.8 32.4 Phate potassium carbonate 0.5 TTMS 0.9587.2 231.0 29.6 Phate lithium percholorate 0.5 TTMS 0.95 88.3 213.7 23.3Phate lithium oxalate 0.5 TTMS 0.95 86.4 246.2 82.0 Phate lithiumcarbonate 0.5 TTMS 0.94 87.2 246.2 36.7 Phate cesium oxalate 0.5 TTMS0.96 86.6 221.4 93.4 Phate cesium nitrate 0.5 TTMS 0.92 84.5 244.5 28.5Phate vinylboronic acid 2- 0.5 TTMS 0.96 87.6 220.3 78.0methyl-2,4-pentanediol Phate ester tris(2,2,2-trifluoroethyl) 0.5 TTMS0.93 83.7 170.4 94.4 borate Phate bis(trimethylene) 0.5 TTMS 0.94 85.7215.3 105.5 diborate Phate bis(neopentyl 0.5 TTMS 0.94 84.3 199.9 80.7glycolato)diboron Phate 2-allyl-5,5-dimethyl- 0.5 TTMS 0.94 87.1 368.8139.8 1,3,2-dioxaborinane Phate diallyl carbonate 0.5 TTMS 0.97 87.6303.0 41.2 Phate bis(pentafluorophenyl) 0.5 TTMS 0.86 76.7 303.7 128.2carbonate Phate N,N-dimethylacetamide 2 TTMS 0.93 85.9 255.5 115.9 Phate1-methyl-2- 0.5 TTMS 0.90 85.8 273.8 42.9 pyrrolidinone Phate4-fluorophenyl 0.5 TTMS 0.94 83.4 279.0 50.3 isocyanate Phate 1,4-butanesultone 0.5 TTMS 0.94 87.9 234.2 38.7 Phate 1-(4,5-dihydro-1,3- 0.5 TTMS0.93 78.0 256.9 23.2 thiazol-2-yl)piperidine Phate oxalate

Combinations notable for their wide temperature range performanceimprovements include tris(trimethylsilyl)phosphate and: sodium nitrate,potassium carbonate, lithium perchlorate, cesium nitrate, or1-(4,5-dihydro-1,3-thiazol-2-yl)piperidine oxalate (structure (n)).

Table 9 summarizes first cycle capacity, coulombic efficiency, lowtemperature performance, and high temperature stability for several lowtemperature additives with trimethylsilyl polyphosphate. Certain of thecombinations, but not the majority of the combinations, show improvementover the control in both low temperature and high temperatureevaluation.

TABLE 9 Low temperature additives with TMSPoly High Cyc1 Cyc Conc. TempCapacity 1 CE −25 C. 2nd Low Temp Additive (wt. %) 0.5 wt % (mAh/cm²)(%) ASI ASI Control - vinylene 0.5 LiBOB 0.96 86.1 385.0 35.0 carbonatesodium percholorate 0.5 TMSPoly 0.93 85.5 237.8 67.7 sodium nitrate 0.5TMSPoly 0.87 78.7 228.5 103.8 potassium carbonate 0.5 TMSPoly 0.96 88.4225.9 47.4 lithium percholorate 0.5 TMSPoly 0.93 86.1 232.1 45.7 lithiumoxalate 0.5 TMSPoly 0.95 86.1 200.9 40.7 lithium carbonate 0.5 TMSPoly0.97 89.1 189.6 23.7 cesium oxalate 0.5 TMSPoly 0.93 86.4 212.2 34.1cesium nitrate 0.5 TMSPoly 0.94 81.7 235.5 36.1 vinylboronic acid 2- 0.5TMSPoly 0.91 82.6 326.4 111.7 methyl-2,4-pentanediol estertris(2,2,2-trifluoroethyl) 0.5 TMSPoly 0.92 86.3 184.5 55.7 boratebis(trimethylene) 0.5 TMSPoly 0.94 85.2 220.0 101.6 diboratebis(neopentyl 0.5 TMSPoly 0.93 82.1 234.2 100.3 glycolato)diboron2-allyl-5,5-dimethyl- 0.5 TMSPoly 0.86 79.5 478.4 127.11,3,2-dioxaborinane diallyl carbonate 0.5 TMSPoly 0.95 86.7 318.2 50.8bis(pentafluorophenyl) 0.5 TMSPoly 0.83 72.3 286.1 107.2 carbonateN,N-dimethylacetamide 2 TMSPoly 0.87 79.0 238.9 88.7 1-methyl-2- 0.5TMSPoly 0.87 80.1 269.4 106.9 pyrrolidinone 4-fluorophenyl 0.5 TMSPoly0.91 81.1 252.3 127.1 isocyanate 1,4-butane sultone 0.5 TMSPoly 0.9484.6 245.4 31.2

Combinations notable for their wide temperature range performanceimprovements include trimethylsilyl polyphosphate and: lithiumcarbonate, cesium oxalate, or 1,4-butane sultone.

While the invention has been described with reference to the specificembodiments thereof, it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,method, or process to the objective, spirit and scope of the invention.All such modifications are intended to be within the scope of the claimsappended hereto. In particular, while the methods disclosed herein havebeen described with reference to particular operations performed in aparticular order, it will be understood that these operations may becombined, sub-divided, or re-ordered to form an equivalent methodwithout departing from the teachings of the invention. Accordingly,unless specifically indicated herein, the order and grouping of theoperations are not limitations of the invention.

1. A rechargeable battery, comprising: an electrolyte formulationcomprising: a lithium salt comprising LiPF₆; an organic solvent; and anadditive comprising a boron-containing compound selected from the groupconsisting of diborons and borates; and a cathode comprising a lithiumion intercalating material, wherein discharge and recharge of thebattery is accomplished by intercalation and de-intercalation of lithiumions into and from the cathode.
 2. The rechargeable battery of claim 1wherein the additive comprises a compound selected from the groupconsisting of tris(2,2,2-trifluoroethyl)borate,bis(neopentylglycolato)diboron, and bis(trimethylene)diborate.
 3. Therechargeable battery of claim 1 wherein the additive comprises tris(2,2,2-trifluoroethyl)borate.
 4. The rechargeable battery of claim 1wherein the additive comprises bis(neopentylglycolato)diboron.
 5. Therechargeable battery of claim 1 wherein the additive comprisesbis(trimethylene)diborate.
 6. The rechargeable battery of claim 3further comprising lithium bis(oxalato)borate as a second additive. 7.The rechargeable battery of claim 4 further comprising lithiumbis(oxalato)borate as a second additive.
 8. The rechargeable battery ofclaim 5 further comprising lithium bis(oxalato)borate as a secondadditive.
 9. The rechargeable battery of claim 3 further comprising4-nitrophenyl 2-(trimethylsilyl)ethyl carbonate as a second additive.10. The rechargeable battery of claim 4 further comprising 4-nitrophenyl2-(trimethylsilyl)ethyl carbonate as a second additive.
 11. Therechargeable battery of claim 5 further comprising 4-nitrophenyl2-(trimethylsilyl)ethyl carbonate as a second additive.
 12. Therechargeable battery of claim 3 further comprising cesium nitrate as asecond additive.
 13. The rechargeable battery of claim 4 furthercomprising cesium nitrate as a second additive.
 14. The rechargeablebattery of claim 5 further comprising cesium nitrate as a secondadditive.
 15. The rechargeable battery of claim 3 further comprisingmaleic anhydride as a second additive.
 16. The rechargeable battery ofclaim 4 further comprising maleic anhydride as a second additive. 17.The rechargeable battery of claim 5 further comprising maleic anhydrideas a second additive.
 18. The rechargeable battery of claim 3 furthercomprising tris(trimethylsilyl)phosphate as a second additive.
 19. Therechargeable battery of claim 4 further comprisingtris(trimethylsilyl)phosphate as a second additive.
 20. The rechargeablebattery of claim 5 further comprising tris(trimethylsilyl)phosphate as asecond additive.
 21. The rechargeable battery of claim 3 furthercomprising trimethylsilyl polyphosphate as a second additive.
 22. Therechargeable battery of claim 4 further comprising trimethylsilylpolyphosphate as a second additive.
 23. The rechargeable battery ofclaim 5 further comprising trimethylsilyl polyphosphate as a secondadditive.
 24. The rechargeable battery of claim 1 wherein the additivecomprises a compound represented by formula (a):

where at least one of R₁, R₂ and R₃ includes a fluorine.
 25. Therechargeable battery of claim 1 wherein the additive comprises acompound represented by formula (b):

where X is oxygen or carbon and, independently, Y is oxygen or carbon.